1. Field of the Invention
The present invention relates to a back print type ink jet recording sheet, and, particularly, to an ink jet recording sheet coping with oily ink.
2. Description of the Related Art
An ink jet recording system is a system in which ink droplets are jetted towards a surface of a recording sheet at a high velocity from an ink exit port (nozzle) of a printer to form a recording image on the surface of the sheet. This system enables high speed character and image printing, makes it easy to attain multi-coloration, is suitable for the recording of a large-scaled image, makes a smaller sound during recording and is reduced in running cost. This is why printers using this system in personal computers used in offices and for household use are being spread rapidly.
Also, because the ink jet recording system is suitable for the recording of a large-scaled image as aforementioned, it is preferably used for the printing on large-scaled sign-boards, posters, illumination sheets and the like used outdoors. However, in conventional ink jet recording systems, aqueous ink is primarily used. As to recording sheets, those for the aqueous ink have been developed. These sheets therefore have the problem of inferior weatherability and water resistance when printing is made on large-scaled sign-boards, posters, illumination sheets and the like using these sheets.
In light of these problems, a back print type recording sheet has been developed which uses a transparent or semitransparent plastic film as its base material and is used in the following system: a reverse image is printed from the side of an ink-receiving layer disposed on the film by using an ink jet system and the printed image is viewed from the side opposite to the printed surface, namely from the substrate side. Recording sheets of this type are advantageous in view of weatherability, water resistance, and the like since the substrate side is made to face outside and are therefore widely spread.
Conventionally, in this back print type, those having a structure in which an intermediate layer is disposed on a substrate and an ink-receiving layer is disposed on the intermediate layer are known. It is designed such that the receiving layer allows ink to permeate and the intermediate layer absorbs the ink. Because ink is absorbed in the side close to the substrate, the back print type has the characteristics that it has high water resistance and the density of the print viewed from the backface is high. For example, back print type ink jet recording sheets in which an ink-absorbing layer and an ink-passing layer are laminated on a light-transmittable substrate are described in Japanese Patent Application Laid-Open No. 10-329410 and Japanese Patent Application Laid-Open No. 10-44586. Because in the recording sheets disclosed in these publications, the plane to be viewed is the surface of a transparent film of the substrate, such an effect that a reduction in glossiness is small and an image similar to a silver salt photograph can be expressed due to subtle light scattering in the transparent film is obtained.
Meanwhile, the use of oily ink has been increased in the ink jet recording system in recent years. This reason is that the oily ink is superior in water resistance, so that the print product can be preferably used outdoors and the problem of the clogging of a nozzle is improved with the development of oily ink bettered in the dispersion of a pigment, the improvement of a printer, and the like.
In view of this, it is considered that a print product superior to that obtained in the case of using aqueous ink in the weatherability, water resistance, and the like is obtained if a back print is made using oily ink.
However, recording sheets used in the conventional back print system is made on the assumption that aqueous ink is used. Therefore, if a print is made on the recording sheet by using oily ink, ink is not absorbed in an intermediate layer, specifically, an ink solvent which is volatilized with difficulty remains at the interface between the ink-receiving layer and the intermediate layer. Hence, the ink-absorbing ability of the recording sheet as a whole is not improved and the ink-receiving layer cannot embrace ink, giving rise to the problem of the occurrence of such a phenomenon (bleeding) that the ink diffuses excessively in a lateral direction (a direction perpendicular to the direction in which ink is jetted).
Accordingly, it is an object of the present invention to provide a new ink jet recording sheet which enables a desirable back print without the occurrence of bleeding even when oily ink is used and which is used in place of an ink jet recording sheet for aqueous ink which is primarily used in a conventional back print system.
The structure of the present invention made to attain the object of solving the above problem is as follows. Specifically, the present invention relates to an ink jet recording sheet comprising an intermediate layer and an ink-receiving layer laminated on a light-transmittable substrate, wherein the intermediate layer is formed of a rubber-based resin, the receiving layer is formed of a hydrophobic resin and a ratio Y/X of reflection density Y of the substrate side to reflection density X of the receiving layer side in a print section when printing is made using oily ink on the receiving layer is 1.0 or more.
Specifically, the inventors of the present invention have made earnest studies based on the fact that when a back print is made using oily ink on a recording sheet for aqueous ink, the absorbing capacity is deficient, leading to the occurrence of bleeding and found that if a rubber-based resin is used for an intermediate layer and this layer is made to absorb a solvent of the oily ink, the ink is absorbed much in the substrate side, so that the print density as viewed from the substrate side is higher without any bleeding. Thus, the present invention has been completed.
In addition to the above structure in the present invention, the rubber-based resin forming the intermediate layer may be a styrene-butadiene resin or a polynorbornene resin.